Method for improving CD micro-loading in photomask plasma etching

ABSTRACT

Embodiments of the present invention provides methods to etching a mask layer, e.g., an absorber layer, disposed in a film stack for manufacturing a photomask in EUV applications and phase shift and binary photomask applications. In one embodiment, a method of etching an absorber layer disposed on a photomask includes transferring a film stack into an etching chamber, the film stack having a chromium containing layer partially exposed through a patterned photoresist layer, providing an etching gas mixture including Cl 2 , O 2  and at least one hydrocarbon gas in to a processing chamber, wherein the Cl 2  and O 2  is supplied at a Cl 2 :O 2  ratio greater than about 9, supplying a RF source power to form a plasma from the etching gas mixture, and etching the chromium containing layer through the patterned photoresist layer in the presence of the plasma.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Application Ser. No.61/783,643 filed Mar. 14, 2013, which is incorporated by reference inits entirety.

BACKGROUND

1. Field

Embodiments of the present invention generally relate to a method forimproving critical dimension (CD) microloading in plasma etching a masklayer and, more specifically, to a method for etching a mask layer(e.g., an absorber layer) for both phase shift and binary photomaskfabrication and EUV photomask fabrication.

2. Description of the Related Art

In the manufacture of integrated circuits (IC), or chips, patternsrepresenting different layers of the chip are created by a chipdesigner. A series of reusable masks, or photomasks, are created fromthese patterns in order to transfer the design of each chip layer onto asemiconductor substrate during the manufacturing process. Mask patterngeneration systems use precision lasers or electron beams to image thedesign of each layer of the chip onto a respective mask. The masks arethen used much like photographic negatives to transfer the circuitpatterns for each layer onto a semiconductor substrate. These layers arebuilt up using a sequence of processes and translate into the tinytransistors and electrical circuits that comprise each completed chip.Thus, any defects in the mask may be transferred to the chip,potentially adversely affecting performance. Defects that are severeenough may render the mask completely useless. Typically, a set of 15 to30 masks is used to construct a chip and can be used repeatedly.

A photomask is typically a glass or a quartz substrate giving a filmstack having multiple layers, including an absorber layer, capping layerand a photomask shift mask layer disposed thereon. When manufacturingthe photomask layer, a photoresist layer is typically disposed on thefilm stack to facilitate transferring features into the film stackduring the subsequently patterning processes. During the patterningprocess, the circuit design is written onto the photomask by exposingportions of the photoresist to extreme ultraviolet light or ultravioletlight, making the exposed portions soluble in a developing solution. Thesoluble portion of the resist is then removed, allowing the exposedunderlying film stack being etched. The etch process removes the filmstack from the photomask at locations where the resist was removed,i.e., the exposed film stack is removed.

With the shrink of critical dimensions (CD), present optical lithographyis approaching a technological limit at the 45 nanometer (nm) technologynode with small features. Next generation lithography (NGL) is expectedto replace the conventional optical lithography method, for example, inthe 32 nm technology node and beyond. There are several NGL candidates,such as extreme ultraviolet (EUV) lithography (EUVL), electronprojection lithography (EPL), ion projection lithography (IPL),nano-imprint, and X-ray lithography. Among these, EUVL is the mostlikely successor due to the fact that EUVL has most of the properties ofoptical lithography, which is more mature technology as compared withother NGL methods.

One of the problems in patterning features with small dimension featuresis the occurrence of a microloading effect, which is a measure of thevariation in etch dimensions between regions of high and low featuredensity. The low feature density regions (e.g., isolated regions)receive more reactive etchants per unit surface area compared to thehigh feature density regions (e.g., dense regions) due to larger totalexpose of surface area in the dense regions, thereby resulting in ahigher etching rate in the low density regions. The sidewall passivationgenerated from the etch by-products exhibited the similar patterndensity dependence where more passivation is formed for the isolatedfeatures due to more by-products being generated in the low featuredensity region. The difference in reactive etchants and the passivationper surface area between these two regions increase as feature densitydifference increase. Thus, due to different etch rates and by-productsformation in high and low feature density regions, it is often observedthat while the low feature density regions have been etched and definedin a certain desired and controlled vertical dimension, the high featuredensity regions are bowed and/or undercut by the lateral attacking dueto the insufficient sidewall passivation or insufficient etchingselectivity of the adjacent layers disposed in the film stack to sustainthe film stack until completion of the etching process. In many cases,the low feature density regions are often etched at a faster rate thanthe high feature density regions, resulting in a deformation, line edgeroughness or tapered top portion of the etched layer in the low featuredensity regions. Insufficient selectivity among the material layersdisposed in the film stack in high and low feature density regions oftenresults in inability to hold critical dimension of the etch features andpoor patterned transfer.

Thus, there is a need for an improved etch process for etching anabsorber layer in a film stack utilized to form a photomask with highetching selectivity.

SUMMARY

Embodiments of the present invention provides methods to etching a masklayer, e.g., an absorber layer, disposed in a film stack formanufacturing a photomask in EUV applications and phase shift and binaryphotomask applications. In one embodiment, a method of etching anabsorber layer disposed on a photomask includes transferring a filmstack into an etching chamber, the film stack having a chromiumcontaining layer partially exposed through a patterned photoresistlayer, providing an etching gas mixture including Cl₂, O₂ and at leastone hydrocarbon gas into a processing chamber, wherein the Cl₂ and O₂ issupplied at a ratio greater than about 9, supplying a RF source power toform a plasma from the etching gas mixture, and etching the chromiumcontaining layer through the patterned photoresist layer in the presenceof the plasma.

In another embodiment, a method of etching an absorber layer disposed ona photomask includes transferring a film stack into an etching chamber,the film stack having an absorber layer partially exposed through apatterned photoresist layer, wherein the absorber layer is a tantalumcontaining layer, providing an etching gas mixture including at least afluorine containing gas and at least one hydrocarbon gas into aprocessing chamber, supplying a RF source power to form a plasma fromthe etching gas mixture, and etching the absorber layer through thepatterned photoresist layer in the presence of the plasma.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 depicts a schematic cross-sectional view of a processing chamberthat may be utilized to fabricate a photomask in accordance with oneembodiment of the present invention;

FIG. 2 depicts a flow diagram of a method for manufacturing a photomaskin accordance with one embodiment of the present invention; and

FIG. 3A-3B depict one embodiment of a sequence for manufacturing an EUVphotomask in accordance with one embodiment of the invention;

FIG. 4 depicts a flow diagram of a method for manufacturing a photomaskin accordance with another embodiment of the present invention; and

FIGS. 5A-5B depict one embodiment of a sequence for manufacturing aphase shift and binary photomask in accordance with one embodiment ofthe invention.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

It is to be noted, however, that the appended drawings illustrate onlyexemplary embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

DETAILED DESCRIPTION

The present invention provides a method and apparatus for etching anabsorber layer for manufacturing a photomask. More specifically, theinvention relates to methods of etching of an absorber layer disposed ona photomask substrate with improved etching selectivity. In oneembodiment, a particular gas mixture including at least a chlorine gas(Cl₂) and oxygen gas (O₂) with a certain predetermined flow rate ratiois utilized to etch a chromium containing layer to form a photomask. Inanother embodiment, another gas mixture including at least a CHF₃ andCF₄ with a certain predetermined flow rate ratio is utilized to etch atantalum containing layer to form a photomask for EUV applications.

FIG. 1 depicts a schematic diagram of an etch reactor 100. Suitablereactors that may be adapted for use with the teachings disclosed hereininclude, for example, the Decoupled Plasma Source (DP^(S)®) II reactor,or the Tetra I, Tetra II, Tetra X Photomask etch systems, all of whichare available from Applied Materials, Inc. of Santa Clara, Calif. Theparticular embodiment of the reactor 100 shown herein is provided forillustrative purposes and should not be used to limit the scope of theinvention. It is contemplated that the invention may be utilized inother plasma processing chambers, including those from othermanufacturers.

The reactor 100 generally comprises a process chamber 102 having asubstrate pedestal 124 within a conductive body (wall) 104, and acontroller 146. The chamber 102 has a substantially flat dielectricceiling or lid 108. Other modifications of the chamber 102 may haveother types of ceilings, e.g., a dome-shaped ceiling. An antenna 110 isdisposed above the ceiling 108 and comprises one or more inductive coilelements that may be selectively controlled (two co-axial elements 110 aand 110 b are shown in FIG. 1). The antenna 110 is coupled through afirst matching network 114 to a plasma power source 112, which istypically capable of producing up to about 3000 W at a tunable frequencyin a range from about 50 kHz to about 13.56 MHz.

The substrate pedestal (cathode) 124 is coupled through a secondmatching network 142 to a biasing power source 140. The biasing source140 generally is a source of up to about 500 W at a frequency ofapproximately 13.56 MHz that is capable of producing either continuousor pulsed power. Alternatively, the biasing source 140 may be a DC orpulsed DC source.

In one embodiment, the substrate support pedestal 124 optionallycomprises an electrostatic chuck 160, which has at least one clampingelectrode 132 and is controlled by a chuck power supply 166. Inalternative embodiments, the substrate pedestal 124 may comprisesubstrate retention mechanisms such as a susceptor clamp ring, amechanical chuck, and the like.

A reticle adapter 182 is used to secure the substrate (e.g., photomaskor reticle), onto the substrate support pedestal 124. The reticleadapter 182 generally includes a lower portion 184 that covers an uppersurface of the pedestal 124 (for example, the electrostatic chuck 160)and a top portion 186 having an opening 188 that is sized and shaped tohold the substrate 101. The opening 188 is generally substantiallycentered with respect to the pedestal 124. The adapter 182 is generallyformed from a single piece of etch resistant, high temperature resistantmaterial such as polyimide ceramic or quartz. An edge ring 126 may coverand/or secure the adapter 182 to the pedestal 124.

A lift mechanism 138 is used to lower or raise the adapter 182 and thesubstrate 101 onto or off of the substrate support pedestal 124. Thelift mechanism 138 comprises a plurality of lift pins 130 (one lift pinis shown) that travel through respective guide holes 136.

A gas panel 120 is coupled to the processing chamber 102 to provideprocess and/or other gases to the interior of the processing chamber102. In the embodiment depicted in FIG. 1, the gas panel 120 is coupledto one or more inlets 116 formed in a channel 118 in the sidewall 104 ofthe chamber 102. It is contemplated that the one or more inlets 116 maybe provided in other locations, for example, in the ceiling 108 of theprocessing chamber 102.

In one embodiment, the gas panel 120 is adapted to provide fluorinatedprocess gas through the inlets 116 and into the interior of the body ofthe processing chamber 102. During processing, a plasma is formed fromthe process gas and maintained through inductive coupling of power fromthe plasma power source 112. The plasma may alternatively be formedremotely or ignited by other methods. In one embodiment, the process gasprovided from the gas panel 120 includes at least a fluorinated gas,chlorine, and a carbon containing gas, an oxygen gas, and an chlorinecontaining gas. Examples of fluorinated and carbon containing gasesinclude CHF₃ and CF₄. Other fluorinated gases may include one or more ofC₂F, C₄F₆, C₃F₈ and C₅F₈. Examples of the oxygen containing gas includeO₂, CO₂, CO, N₂O, NO₂, O₃, H₂O, and the like. Examples of the chlorinecontaining gas include HCl, Cl₂, CCl₄, CHCl₃, CH₂Cl₂, CH₃Cl, and thelike. Suitable examples of the carbon containing gas include methane(CH₄), ethane (C₂H₆), ethylene (C₂H₄), and the like.

The pressure in the processing chamber 102 is controlled using athrottle valve 162 and a vacuum pump 164. The vacuum pump 164 andthrottle valve 162 are capable of maintaining chamber pressures in therange of about 1 to about 20 mTorr. The temperature of the wall 104 maybe controlled using liquid-containing conduits (not shown) that runthrough the wall 104. Typically, the chamber wall 104 is formed from ametal (e.g., aluminum, stainless steel, and the like) and is coupled toan electrical ground 106. The process chamber 102 also comprisesconventional systems for process control, internal diagnostic, end pointdetection, and the like. Such systems are collectively shown as supportsystems 154.

In operation, the temperature of the substrate 101 is controlled bystabilizing the temperature of the substrate pedestal 124. In oneembodiment, the substrate support pedestal 124 comprises a resistiveheater 144 and a heat sink 128. The resistive heater 144 generallycomprises at least one heating element 134 and is regulated by a heaterpower supply 168. A backside gas (e.g., helium (He)) from a gas source156 is provided via a gas conduit 158 to channels that are formed in thepedestal surface under the substrate 101. The backside gas is used tofacilitate heat transfer between the pedestal 124 and the substrate 101.During processing, the pedestal 124 may be heated by the embeddedresistive heater 144 to a steady-state temperature, which in combinationwith the helium backside gas, facilitates uniform heating of thesubstrate 101. Using such thermal control, the substrate 101 may bemaintained at a temperature between about 0 and 550 degrees Celsius.

An optional ion-radical shield 170 is disposed in the chamber 102 abovethe pedestal 124. The ion-radical shield 170 is electrically isolatedfrom the chamber sidewalls 104 and the pedestal 124 such that no groundpath from the plate to ground is provided. In other embodiments, theion-radical shield 170 may be biased or electrically floating. Oneembodiment of the ion-radical shield 170 comprises a substantially flatplate 172 and a plurality of legs 176 supporting the plate 172. Theplate 172, which may be made of a variety of materials compatible withprocess needs, comprises one or more openings (apertures) 174 thatdefine a desired open area in the plate 172. This open area controls theamount of ions that pass from a plasma formed in an upper process volume178 of the process chamber 102 to a lower process volume 180 locatedbetween the ion-radical shield 170 and the substrate 101. The greaterthe open area, the more ions can pass through the ion-radical shield170. As such, the size of the apertures 174 controls the ion density involume 180, and the shield 170 serves as an ion filter. The plate 172may also comprise a screen or a mesh wherein the open area of the screenor mesh corresponds to the desired open area provided by apertures 174.Alternatively, a combination of a plate and screen or mesh may also beused.

During processing, a potential develops on the surface of the plate 172as a result of electron bombardment from the plasma. The potentialattracts ions from the plasma, effectively filtering them from theplasma, while allowing neutral species, e.g., radicals, to pass throughthe apertures 174 of the plate 172. Thus, by reducing the amount of ionsthrough the ion-radical shield 170, etching of the mask by neutralspecies or radicals can proceed in a more controlled manner. Thisreduces erosion of the resist as well as sputtering of the resist ontothe sidewalls of the patterned material layer, thus resulting inimproved etch bias and critical dimension uniformity.

A controller 146 is coupled to the processing chamber 100 to controloperation of the processing chamber 100. The controller 146 includes acentral processing unit (CPU) 150, a memory 148, and a support circuit152 utilized to control the process sequence and regulate the gas flowsfrom the gas panel 120. The CPU 150 may be any form of general purposecomputer processor that may be used in an industrial setting. Thesoftware routines can be stored in the memory 148, such as random accessmemory, read only memory, floppy, or hard disk drive, or other form ofdigital storage. The support circuit 152 is conventionally coupled tothe CPU 150 and may include cache, clock circuits, input/output systems,power supplies, and the like. Bi-directional communications between thecontroller 146 and the various components of the processing system 100are handled through numerous signal cables.

FIG. 2 is a flow diagram of one embodiment of a method 200 for etchingan absorber layer formed in a film stack disposed on a photomask thatmay be performed in a processing chamber, such as the processing chamber100 depicted in FIG. 1. FIGS. 3A-3B are schematic cross-sectional viewillustrating a sequence for etching an absorber layer for manufacturingan EUV photomask according to the method 200. Although the method 200 isdescribed below with reference to a substrate utilized to fabricate aphotomask, the method 200 may also be used to advantage in otherphotomask etching or any etching applications.

The method 200, which may be stored in computer readable form in thememory 148 of the controller 146 or other storage medium, begins atblock 202 when the photomask substrate 101 is transferred to and placedon a support pedestal 124 disposed in an etch reactor, such as the etchreactor 100 depicted in FIG. 1.

The method 200 begins at block 202 by providing a substrate into aprocessing chamber, such as the substrate 101 into the processingchamber 100 depicted in FIG. 1. The substrate 101 may be an opticallytransparent silicon based material, such as quartz (i.e., silicondioxide (SiO₂)) layer, having a film stack 300 disposed on the substrate101 that may be utilized to form desired features 318 in the film stack300. As shown in the exemplary embodiment depicted in FIG. 3A, thesubstrate 101 may be a quartz substrate (i.e., low thermal expansionsilicon dioxide (SiO₂)) layer. The substrate 101 may have a rectangularshape having sides between about 5 inches to about 9 inches in length.The substrate 101 may be between about 0.15 inches and about 0.25 inchesthick. In one embodiment, the substrate 101 is about 0.25 inches thick.An optional chromium containing layer 304, such as a chromium nitride(CrN) layer may be disposed to a backside 302 of the substrate 101 asneeded.

An EUV reflective multi-material layer 306 is disposed on the substrate101. The reflective multi-material layer 306 may include at least onemolybdenum layer 306 a and at least one silicon layer 306 b. Althoughthe embodiment depicted in FIG. 3A shows five pairs of molybdenum layer306 a and a silicon layer 306 b (alternating molybdenum layers 306 a andthe silicon layers 306 b repeatedly formed on the substrate 101), it isnoted that number of molybdenum layers 306 a and the silicon layers 306b may be varied based on different process needs. In one particularembodiment, forty pairs of molybdenum layers 306 a and the siliconlayers 306 b may be deposited to form the reflective multi-materiallayer 306. In one embodiment, the thickness of each single molybdenumlayer 306 a may be controlled at between about 1 Å and about 10 Å, suchas about 3 Å, and the thickness of the each single silicon layer 306 bmay be controlled at between about 1 Å and about 10 Å, such as about 4Å. The reflective multi-material layer 306 may have a total thicknessbetween about 10 Å and about 500 Å. The reflective multi-material layer306 may have an EUV light reflectivity of up to 70% at 13.5 nmwavelength. The reflective multi-material layer 306 may have a totalthickness between about 70 nm and about 140 nm.

Subsequently, a capping layer 308 is disposed on the reflectivemulti-material layer 306. The capping layer 308 may be fabricated by ametallic material, such as ruthenium (Ru) material, zirconium (Zr)material, or any other suitable material. In the embodiment depicted inFIG. 3A, the capping layer 308 is a ruthenium (Ru) layer. The cappinglayer 308 may have a thickness between about 1 nm and about 10 nm.

An absorber layer 316 may then be disposed on the capping layer 308. Theabsorb layer 316 is an opaque and light-shielding layer configured toabsorb a portion of the light generated during the lithography process.The absorber layer 316 may be in form of a single layer or a multi-layerstructure, such as including a self-mask layer 312 disposed on a bulkabsorber layer 310, as the embodiments depicted in FIGS. 3A-3B. In oneembodiment, the absorber layer 316 has a total film thickness betweenabout 50 nm and about 200 nm. The total thickness of the absorber layer316 advantageously facilitates meeting the strict overall etch profiletolerance for EUV masks in sub-45 nm technology node applications.

In one embodiment, the bulk absorber layer 310 may comprisetantalum-based materials with essentially no oxygen, for exampletantalum silicide based materials, such as TaSi or TaSiN, nitrogenizedtantalum boride-based materials, such as TaBN, and tantalumnitride-based materials, such as TaN. The self-mask layer 312 may befabricated from a tantalum and oxygen-based materials. The compositionof the self-mask layer 312 corresponds to the composition of the bulkabsorber layer 310 and may comprise oxidized and nitrogenized tantalumand silicon based materials, such as TaSiON, when the bulk absorberlayer 310 comprises TaSi or TaSiN; tantalum boron oxide based materials,such as TaBO, when the bulk absorber layer 310 comprises TaBN; andoxidized and nitrogenized tantalum-based materials, such as TaON or TaO,when the bulk absorber layer 310 comprises TaN.

A patterned photoresist layer 314 is then formed over the absorber layer316 having openings 318 formed therein that expose portions 320 of theabsorber layer 316 for etching. The openings 318 of the photoresistlayer 314 may be patterned by a gas mixture including at least a H₂ gasand a N₂ gas. During patterning of the photoresist layer 314, a RFsource power may be supplied to a coil formed in a processing chamber,such as the etch reactor 100 which will be further described below withreferenced to FIG. 1, with or without applying a bas RF power to etchthereof forming the openings 318 in the photoresist layer 314. Thephotoresist layer 314 may comprise any suitable photosensitive resistmaterials, such as an e-beam resist (for example, a chemically amplifiedresist (CAR)), and deposited and patterned in any suitable manner. Thephotoresist layer 314 may be deposited to a thickness between about 100nm and about 1000 nm.

At block 204, an etching gas mixture is supplied into the etch reactorto etch the portions 320 of the absorber layer 316 exposed by thepatterned photoresist layer 314, as shown in FIG. 3A. The self-masklayer 312 and the bulk absorber layer 310 included in the absorber layer316 may be continuously etched using one process step, such as a singleetchant chemistry, or separately etched by multiple steps in one ordifferent etching processes as needed. The patterns from the photoresistlayer 314 are then transferred into the absorber layer 316 through theetching process.

In one embodiment, the self-mask layer 312 and the bulk absorber layer310 included in the absorber layer 316 may be continuously etched usingone process step. The etching gas mixture supplied to etch the absorberlayer 316 includes at least a fluorine containing gas. Suitable examplesof the fluorine containing gas includes CF₄, CHF₃, CH₂F₂, C₂F₆, C₂F₈,SF₆, NF₃ and the like. As the fluorine element is an aggressive etchant,the fluorine containing gas supplied in the etching gas mixture isutilized to etch away portions of the absorber layer 316, including boththe self-mask layer 312 and the bulk absorber layer 310 to form desiredfeatures 318 into the absorber layer 316. In one embodiment, the etchinggas mixture supplied to etch the absorber layer 316 includes at least aCF₄ gas and a CHF₃ gas.

Additionally, a hydrocarbon gas may also be added to the etching gasmixture to assist etching the absorber layer 316 as needed. Examples ofthe hydrocarbon gas include CH₄, C₂H₆, C₃H₈, combinations thereof andthe like. It is believed that hydrocarbon gas may provide a polymersource to assist passivating sidewalls of the features being etchedduring the etching process. In an alternative embodiment, an inert gasmay also be supplied into the etching gas mixture to assist the profilecontrol as needed. Examples of the inert gas supplied in the gas mixtureinclude Ar, He, Ne, Kr, Xe or the like.

In one embodiment, CF₄ gas and CHF₃ gas supplied in the etching gasmixture may be maintained at a predetermined ratio to yield an efficientetching rate, along with the hydrocarbon gas as supplied, whilesufficiently protecting the sidewall from undesired etching. In anexemplary embodiment, the CHF₃ gas and CF₄ gas is supplied in theetching gas mixture at a CHF₃:CF₄ ratio of greater than about 9, such asbetween about 10:1 and about 20:1. In another embodiment, CF₄ gas andCHF₃ gas is supplied in the etching gas mixture at a CHF₃:CF₄ betweenabout 1:1 to about 10:1. Alternatively, CF₄ gas may be supplied at aflow rate by volume between about 1 sccm and about 100 sccm. CHF₃ gasmay be supplied at a flow rate by volume between about 10 sccm and about100 sccm.

Furthermore, the hydrocarbon supplied in the etching gas mixture mayalso be supplied at a predetermined ratio in the etching gas mixture toimprove etching efficiency and performance. In on embodiment, thehydrocarbon gas, such as CH₄ gas, supplied in the total etching gasmixture may be between about 2 percent and about 20 percent.Alternatively, the hydrocarbon gas may be supplied at a flow rate byvolume between about 1 sccm and about 40 sccm.

At block 306, after the etching gas mixture is supplied into the etchinggas mixture, a RF power is supplied to form a plasma from the gasmixture therein to etch the absorber layer 316. The RF source power maybe supplied at the gas mixture between about 100 Watts and about 3000Watts and at a frequency between about 400 kHz and about 13.56 MHz. Abias power may also be supplied as needed. The bias power may besupplied at between about 10 Watts and about 300 Watts. In oneembodiment, the RF source power may be pulsed with a duty cycle betweenabout 10 to about 95 percent at a RF frequency between about 500 Hz andabout 10 kHz.

Several process parameters may also be controlled while supplying theetching gas mixture to perform the etching process. The pressure of theprocessing chamber may be controlled at between about 0.5 milliTorr andabout 500 milliTorr, such as between about 1 milliTorr and about 20milliTorr.

The etching process is performed to etch the absorber layer 316 until anupper surface 322 of the underlying capping layer 308 is exposed, asshown in FIG. 3B. The end point of the etching process may be controlledby time mode or other suitable methods. For example, the etching processmay be terminated after performing between about 50 seconds and about500 seconds until the upper surface 322 of the underlying capping layer308 is exposed. In this particular embodiment, the etching process maybe performed between about 1 seconds and about 1000 seconds. In anotherembodiment, the etching process may be terminated by determination froman endpoint detector, such as an OES detector or other suitable detectoras needed.

After the desired profile and/or the structure of the film stack 300 isformed on the substrate 101, the photoresist layer 314 may be removed.In one embodiment, the remaining resist and protective layer is removedby ashing. The removal process may be performed in-situ the etch reactor100 in which the etching process performed at block 202-206 wasperformed. In the embodiment wherein the photoresist layer 314 iscompletely consumed during the etching process, the ashing orphotoresist layer removal process may be eliminated.

FIG. 4 is a flow diagram of one embodiment of a method 400 for etchingan absorber layer formed in a film stack having a patterned photoresistlayer disposed thereon on a photomask substrate, such as an absorberlayer 504 formed in a film stack 501 having a patterned photoresistlayer 506 disposed on the substrate 101 depicted in FIG. 5A.

Similar to the description above, the substrate 101 may be an opticallytransparent silicon based material, such as quartz (i.e., silicondioxide (SiO₂)) layer. In the exemplary embodiment depicted in FIG. 5A,the substrate 101 may be a quartz substrate (i.e., low thermal expansionsilicon dioxide (SiO₂)) layer. The substrate 101 has a rectangular shapehaving sides between about 5 inches to about 9 inches in length. Thesubstrate 101 may be between about 0.15 inches and about 0.25 inchesthick. In one embodiment, the substrate 101 is about 0.25 inches thick.

The film stack 501 disposed on the substrate 101 that may be utilized toform desired features (i.e., openings 508) in the film stack 501.Although the method 400 is described below with reference to a substrateutilized to fabricate a photomask, the method 400 may also be used toadvantage in other photomask etching or any etching application.

The method 400 begins at block 402 when the substrate 101 is transferredto and placed on a substrate support member disposed in an etch reactor,such as the etching chamber 100 depicted in FIG. 1. The film stack 501disposed on the substrate 101 includes an absorber layer 504 defined bythe patterned photoresist layer 506 having portions 510 of the absorberlayer 504 exposed by the patterned photoresist layer 506 readily foretching, as shown in FIG. 5A. In one embodiment, a phase shift masklayer 502 may be disposed between the substrate 101 and the absorberlayer 504.

In one embodiment, the absorber layer 504 may be a metal containinglayer, e.g., a chromium containing layer, such as a Cr metal, chromiumoxide (CrO_(x)) chromium nitride (CrN) layer, chromium oxynitride(CrON), or multilayer with these materials, as needed. The phase shiftmask layer 502 may be a molybdenum containing layer, such as Mo layer,MoSi layer, MoSiN, MoSiON, and the like. The patterned photoresist layer506 is then formed over the absorber layer 504 having openings 508formed therein that expose portions 510 of the absorber layer 504 foretching.

At block 404, an etching gas mixture is supplied into the processingchamber 100 to etch the absorber layer 504. The patterned photoresistlayer 506 may serve as a mask layer to protect some portion of theabsorber layer 504 from being etched during the absorber layer etchingprocess.

In one embodiment, a chlorine containing gas may be supplied in theetching gas mixture used for etching an absorber layer (e.g., a chromiumcontaining layer). Examples of the chlorine containing gas include HCl,Cl₂, CCl₄, CHCl₃, CH₂Cl₂, CH₃Cl, and the like. An oxygen containing gasmay also supplied in the etching gas mixture during the etching process.Examples of the oxygen containing gas include O₂, CO₂, CO, N₂O, NO₂, O₃,H₂O, and the like. Alternatively, a hydrocarbon gas, such as CH₄, C₂H₆,C₃H₈, combinations thereof and the like, may also be supplied in theetching gas mixture as needed. It is believed that hydrocarbon gas mayprovide a polymer source to assist passivating sidewalls of the featuresbeing etched during the etching process. In an alternative embodiment,an inert gas may also be supplied into the etching gas mixture to assistthe profile control as needed. Examples of the inert gas supplied in thegas mixture include Ar, He, Ne, Kr, Xe or the like.

In one embodiment, the etching gas mixture including Cl₂ and O₂ may beused to etch the absorber layer 504, such as a chromium containinglayer. The Cl₂ gas and O₂ gas supplied in the etching gas mixture may bemaintained at a predetermined ratio to yield an efficient etching rate,along with the hydrocarbon gas as supplied, while sufficientlyprotecting the sidewall from undesired etching. In an exemplaryembodiment, the Cl₂ gas and O₂ gas is supplied in the etching gasmixture at a Cl₂:O₂ ratio greater than about 9, such as between about10:1 and about 20:1. Alternatively, the Cl₂ gas may be supplied at aflow rate by volume between about 50 sccm and about 300 sccm. The O₂ gasmay be supplied at a flow rate by volume between about 5 sccm and about100 sccm.

Furthermore, the hydrocarbon supplied in the etching gas mixture mayalso be supplied at a predetermined ratio in the etching gas mixture toimprove etching efficiency and performance. In on embodiment, thehydrocarbon gas, such as CH₄ gas, supplied in the total etching gasmixture may be controlled at between about 2 percent and about 20percent at flow volume. Alternatively, the hydrocarbon gas may besupplied at a flow rate by volume between about 1 sccm and about 40sccm.

At block 406, after the etching gas mixture is supplied into the etchinggas mixture, RF power is supplied to form a plasma from the etching gasmixture therein to etch the absorber layer 504. The RF source power maybe supplied at the gas mixture between about 100 Watts and about 3000Watts and at a frequency between about 400 kHz and about 13.56 MHz. Abias power may also be supplied as needed. The bias power may besupplied at between about 10 Watts and about 300 Watts. In oneembodiment, the RF source power may be pulsed with a duty cycle betweenabout 10 to about 95 percent at a RF frequency between about 500 Hz andabout 10 kHz.

Several process parameters may also be controlled while supplying theetching gas mixture to perform the etching process. The pressure of theprocessing chamber may be controlled at between about 0.5 milliTorr andabout 500 milliTorr, such as between about 1 milliTorr and about 20milliTorr.

The etching process is performed to etch the absorber layer 504 until anupper surface 512 of the underlying phase shift mask layer 502 isexposed, as shown in FIG. 5B. The end point of the etching process maybe controlled by time mode or other suitable methods. For example, theetching process may be terminated after performing between about 50seconds and about 500 seconds until the upper surface 512 of theunderlying phase shift mask layer 502 is exposed. In this particularembodiment, the etching process may be performed between about 1 secondsand about 500 seconds. In another embodiment, the etching process may beterminated by determination from an endpoint detector, such as an OESdetector or other suitable detector as needed.

It is believed utilizing a predetermined ratio of reactive etchantssupplied in an etching gas mixture may provide high selectivity for theabsorber layer to the adjacent layers during an etching process. Byefficiently improving etching selectivity of the absorber layer to otheradjacent layers in the film stack, the photomask layer may sustain alonger time during an etching until completion of the features aretransferred to the absorber layer so that the micro-loading effect maybe efficiently eliminated or improved.

Thus, a method for etching an absorber layer, such as a Cr containinglayer or a Ta containing layer has been provided that advantageouslyimproves etching selectivity, trench attributes and profile overconventional processes. Accordingly, the method of etching an absorberlayer described herein advantageously facilitates fabrication ofphotomasks suitable for patterning features having small criticaldimensions in EUV technologies and phase shift and binary photomaskapplications.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

The invention claimed is:
 1. A method of etching an absorber layerdisposed on a photomask, comprising: transferring a film stack disposedon a substrate into an etching chamber, the film stack having a chromiumcontaining layer partially exposed through a patterned photoresistlayer; providing an etching gas mixture including Cl₂, O₂ and at leastone hydrocarbon gas in to a processing chamber, wherein the Cl₂ and O₂gases are supplied at a flow rate Cl₂:O₂ ratio between about 10:1 to20:1 and the hydrocarbon gas is supplied between 2 percent and about 20percent to the etching gas mixture by volume; supplying a RF sourcepower to form a plasma from the etching gas mixture; and etching thechromium containing layer through the patterned photoresist layer in thepresence of the plasma.
 2. The method of claim 1, wherein a molybdenumcontaining layer is disposed between the chromium containing layer andthe substrate.
 3. The method of claim 2, wherein the molybdenumcontaining layer is at least one of a Mo layer, MoSi layer, MoSiN layer,and MoSiON layer.
 4. The method of claim 1, wherein the chromiumcontaining layer is at least one of a Cr metal, chromium oxide(CrO_(x)), chromium nitride (CrN) layer, and chromium oxynitride (CrON).5. The method of claim 1, wherein the hydrocarbon gas is at least one ofCH₄, C₂H₆, and C₃H₈.
 6. The method of claim 1, wherein supplying thesource RF power further comprises: providing a plasma source power ofbetween about 100 to about 3000 Watts.
 7. The method of claim 1, whereinsupplying the RF power further comprises: providing a plasma bias powerof between about 10 to about 300 Watts.
 8. A method of etching anabsorber layer disposed on a photomask, comprising: transferring a filmstack disposed on a substrate into an etching chamber, the film stackhaving a chromium containing layer disposed on a molybdenum containinglayer, wherein the chromium containing layer is partially exposedthrough a patterned photoresist layer; providing an etching gas mixtureincluding Cl₂, O₂ and at least one hydrocarbon gas in to a processingchamber, wherein the Cl₂ and O₂ gases are supplied at a flow rate Cl₂:O₂ratio between about 10:1 to 20:1 and the hydrocarbon gas is suppliedbetween 2 percent and about 20 percent to the etching gas mixture byvolume; supplying a RF source power to form a plasma from the etchinggas mixture; providing a plasma bias power of between about 10 Watts andabout 300 Watts; and etching the chromium containing layer through thepatterned photoresist layer in the presence of the plasma.